10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Aerosol Acidity Measurement Using Colorimetry Coupled with a UV-Visible Micro-spectrometer and Its Application to Measurements of Organosulfates in Ambient Air
SHIQI SUN, Myoseon Jang, University of Florida
Abstract Number: 1088 Working Group: Aerosol Chemistry
Abstract Although SO2 concentration has been reduced in USA for last two decades, the acidic aerosol produced from the oxidation of SO2 is still an existing problem in many countries (i.e., Asia and South America) who rely on coal for heating and industries. Sulfate significantly contributes to total fine particulate matter, and yet the prediction of aerosol acidity remains inadequate. Atmospheric aerosol acidity influences the health effects of particulates due to metal solubility, and is also a kinetic model parameter that processes acid-catalytic reactions of atmospheric organics and organosulfate formation to increase secondary organic aerosols. Our laboratory’s recent research efforts have improved the state-of-the science-art via the development of colorimetry integrated with a Reflectance UV-Visible spectrometer (C-RUV). In this study, a portable C-RUV device in the field is developed using a micro-spectrometer that is self-contained and deployable. The C-RUV technique operates by passing an air sample through a filter infused with an indicator (i.e. metanil yellow), which changes color in response to acidity changes. The optical probe transfers both the source beam from the micro-spectrometer to the filter surface through the optical fiber, and the reflected beam from the filter to the detector in the micro-spectrometer. The proton ([H+], mol/L of aerosol) measurement by the C-RUV method has been calibrated for inorganic aerosols comprised of ammonium and sulfate under varied humidity conditions using a flow tube. The resulting C-RUV device and the calibration equation are applied to quantify [H+] in the ambient air. The acidity aerosol can be modulated by both neutralization of sulfuric acid with ammonia and the formation of organosulfate in aerosol. The concentration of organosulfate in aerosol is also estimated by using the difference in proton concentrations obtained from C-RUV and a particle into liquid sampler ion chromatography (PILS-IC) in ambient air. The aerosol acidity measurement using C-RUV device is able to improve the modeling of aerosol formation and the prediction of aerosol hygroscopicity.